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Discussion Starter · #1 ·
Who would any of you recommend to repair threads on a SCAR 17s barrel? I am actually thinking of just having it cut down to 14.5-15” and pin/weld the FH on as well.

To make a long story short, I use a Surefire FH and SOCOM 762 can. I had a very prominent smith install it. It is no longer concentric. I believe the threads are not concentric, as I removed the FH and checked it without the installed shoulder ring and Surefire shims.

I really wish FN made these barrels with a larger shoulder. I’m seriously thinking about just buying a Deadshot barrel.
 

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If you're only concerned with chasing the threads a proper size and pitch die will do that. If the factory threads are not concentric with the bore which is difficult to fathom the only solution would be to chop the threads off and start over.

The bigger question is, how did you determine the barrel's threads are causing concentricity problems?

As others have said Jarod at PMM is well known for quality work...
 

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Discussion Starter · #6 ·
If you're only concerned with chasing the threads a proper size and pitch die will do that. If the factory threads are not concentric with the bore which is difficult to fathom the only solution would be to chop the threads off and start over.

The bigger question is, how did you determine the barrel's threads are causing concentricity problems?

As others have said Jarod at PMM is well known for quality work...
I removed the flash hider, shoulder ring and shims. I screwed back on the FH and mounted the Surefire SOCOM 762. I then inserted a Geissele alignment rod. It is still off but not nearly as bad as it was mounted.

When I mount the Surefire SOCOM 762 on my 5.56 ARs I run suppressed, it’s concentric. I checked it again with a 5.56 Geissele alignment rod. When I mount my Surefire Genesis can on my Tikka, it’s concentric with the 762 Geissele alignment rod.

When I install the original washer that came with the PWS muzzle brake on my rifle (way back from 2012), add the Surefire FH and SOCOM can, it’s still slightly off when measured with the Geissele rod.

Not sure what else it would be. Geissele makes good alignment rods along with all of their parts. My other 5.56 Surefire equipped ARs are all concentric (Daniel Defense, Geissele uppers with surefire FHs). My Galil ACE 7.62x39 SBR is concentric as well when using the same SOCOM 7.62 can and Geissele rod.

You are correct, I was thinking chop barrel to 14.5-15” and pin/weld on Surefire FH. I’d like to get 10k rounds out of the FN barrel if I can, as I shoot mostly M80 ball out of my SCAR. My Tikka eats the match ammo (it’s a CTR that sits in a KRG Whiskey chassis).

Again, I don’t understand why FN doesn’t put a decent shoulder on these barrels.
 

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As bizarre as it would be for a company that's been making barrels for as long and as well as Herstal has it sounds to me like your bore isn't straight. If my suspicion is correct no amount of chopping and threading will work. You can check this yourself with a micrometer by measuring the thickness from bore I.D. to barrel O.D. at the muzzle if it's off at all the barrel is the culprit. A barrel is threaded in a production capacity with an annular cutter followed by a die not a lathe and a die is self-centering therefore it's nearly impossible for the threads to be anything other than concentric with the barrels center. However, a barrel can be bored out of longitudinal alignment with it's true center axis. A micrometer will definitely confirm this.

Another potential issue could be the miniscule shoulder the SCAR's pencil barrel has. If the shoulder isn't completely square with the bore's center any muzzle device will skew under tension. For this you could check by simply screwing on the FH without contacting the shoulder then check with the rod. If the shoulder's bad that's an easy fix with a lathe.
 
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Discussion Starter · #8 ·
As bizarre as it would be for a company that's been making barrels for as long and as well as Herstal has it sounds to me like your bore isn't straight. If my suspicion is correct no amount of chopping and threading will work. You can check this yourself with a micrometer by measuring the thickness from bore I.D. to barrel O.D. at the muzzle if it's off at all the barrel is the culprit. A barrel is threaded in a production capacity with an annular cutter followed by a die not a lathe and a die is self-centering therefore it's nearly impossible for the threads to be anything other than concentric with the barrels center. However, a barrel can be bored out of longitudinal alignment with it's true center axis. A micrometer will definitely confirm this.

Another potential issue could be the miniscule shoulder the SCAR's pencil barrel has. If the shoulder isn't completely square with the bore's center any muzzle device will skew under tension. For this you could check by simply screwing on the FH without contacting the shoulder then check with the rod. If the shoulder's bad that's an easy fix with a lathe.
That’s what I did. It looks off center still.

I hope the bore is not off. That would suck.
 

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SCAR barrels initially have a bore drilled for the mandrel to fit into so it can be hammer forged...unless FN's mandrel is out of spec (which it could be)...I don't see how the barrel could out of centricity....sometimes chrome lining isn't concentric...which could happen...however you would be able to see that looking down the bore...

A barrel doesn't go "out of centricity" unless some really sever neglect has happened somehow...

If it isn't concentric now...it wasn't concentric to begin with...
 

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Discussion Starter · #14 ·
Check with Dave Wilson does excellent pin and welds and quick turn around
He emailed me back today. He basically said he has seen many barrels like mine. After a couple of thousand rounds, the shoulder deforms. Hence, I need a flash hider or muzzle brake that indexes to the muzzle rather than the shoulder of the barrel.

Using Google, there was a thread on this forum that addresses this, and apparently Surefire made a muzzle brake/FH just for the SCAR 20 program that indexes to the muzzle


Problem is, I'm uncertain if they make anything compatible with my Surefire SOCOM 762 can (the original one, Manufactured in 2013). We'll see what they say. I'll try calling them again tomorrow after work since I'm on EST and they're on PST.

I showed Dave pictures, but he didn't address it in terms of cutting the barrel and pinning it. I'm not even sure what gas jet I would need if the barrel was cut to 14.5-15". I would like to get a few more thousand rounds out of the barrel before buying something else. A Deadshot barrel is appealing, but you lose the SCAR's gas block for an AR-10 style adjustable gas block (set screw to secure, screw to adjust gas flow). Not sure if I like that idea.

I did finally get my OSS 762 can. I'll have to read about their FH to see if it indexes the muzzle vs shoulder.
 

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Discussion Starter · #15 ·
 

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The Surefire FH762K-SCAR-HC is for use with their pre SOCOM suppressors and I don't believe they will work with the 2013 and after SF SOCOM suppressors. I have two 2012 FA762K suppressors and this is the correct FH for them .
If you look at my rifle and the barrel assemblies you can see that no timing shims are needed and the flats on the
flash hiders are in different positions.
Air gun Trigger Machine gun Gun barrel Gun accessory
 

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Discussion Starter · #17 ·
The Surefire FH762K-SCAR-HC is for use with their pre SOCOM suppressors and I don't believe they will work with the 2013 and after SF SOCOM suppressors. I have two 2012 FA762K suppressors and this is the correct FH for them .
If you look at my rifle and the barrel assemblies you can see that no timing shims are needed and the flats on the
flash hiders are in different positions.
View attachment 149635
So they made it right the first time but now they don’t offer it. How annoying. I will try contacting Surefire again.
 

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This could be your solution.
 

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Discussion Starter · #19 ·
This could be your solution.
I had that ring on there and PMM installed it. It is no longer concentric with use.
 

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Discussion Starter · #20 ·
Update: I sent the flash hider, barrel and suppressor to Surefire. They wanted to look over everything. Marvin Pitts called me and said he would work on my barrel as well. We’ll see what Surefire says.
 
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